Process for producing ammonium salts

ABSTRACT

In one embodiment, the invention is to a process for producing an ammonium salt composition. The process comprises the step of providing a process stream comprising sulfuric acid, methylene dichloride, and a tertiary amine or a precursor thereof. The process further comprises the step of contacting the process stream with ammonia under conditions effective to form a product stream and a waste stream. The product stream comprises the ammonium salt and the waste stream comprises water, methylene dichloride, ammonia, and the tertiary amine. The process further comprises the step of deriving from the waste stream an off gas stream comprising ammonia and a first amount of methylene dichloride. The process also comprises the step of contacting at least a portion of the off gas stream or a derivative thereof with an adsorbent under conditions effective to separate at least a portion of the off gas into a methylene dichloride stream comprising methylene dichloride.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/428,477, filed on Dec. 30, 2010; European Patent Application No.10160272.0, filed on Apr. 19, 2010; European Patent Application No.10160275.3, filed on Apr. 19, 2010; and European Patent Application No.10160278.7, filed on Apr. 19, 2010, the entire contents and disclosuresof which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to the production of ammoniumsalts. More specifically, the present invention relates to theproduction of ammonium sulfate and the recovery of tertiary organicamines and solvent from a process stream comprising sulfuric acid.

BACKGROUND OF THE INVENTION

Many conventional chemical processes yield process waste streamscomprising sulfuric acid, organic tertiary amines, and solvents. Theorganic tertiary amines are commercially valuable and, as a consequence,it is desirable to recover the tertiary amines from the sulfuric acid.In addition, the waste sulfuric acid may be converted to ammoniumsulfate, which may be used, for example, in the fertilizer industry.Also, the solvents that remain may be recovered and/or re-used.

DE 101 46 689 teaches one exemplary method that utilizes distillation torecover organic amines from catalyst waste stream that contains amines.DE 35 22 470 A discloses the recovery of amine and metallic componentsin a polyphenylene ether synthesis waste stream via the use of a causticsoda. DE 44 16 571 discloses the recovery of amines from acidic streamby the addition of alkali bases followed by distillation until dry.

In addition, CN 1883790 describes the recovery of amines byneutralization with inorganic bases of oxide origin, e.g., NaOH, KOH,Ca(OH)₂, or CaCO₃. In this method, the sulfates that are created in sidereactions must either be disposed of or processed using large amounts ofenergy, e.g., evaporation or drying, in order to obtain a usableproduct. Also, due to the molar masses of the oxide used in thereaction, the bases are often used in high amounts. In case of calciumbases, the calcium sulfate that is created precipitates during thereaction and, as such, the suspension must either be diluted orthoroughly blended, which adds to the separation cost.

Typically, when utilized as a fertilizer, an ammonium sulfatecomposition should comprise a low total amount of organic compounds(“TOC”). DE 35 45 196 A1 discloses the use of ammonia in a process torecover 1.) tertiary aliphatic amines, and 2.) ammonium sulfate fromwaste sulfuric acid. The yield of the tertiary amines recovered by thisprocess, however, is low and, as a consequence, the TOC remaining in theammonium sulfate is too high. Thus, this process requires furtherpurification to reduce the TOC in the dry ammonium sulfate to anacceptable level. In addition to keeping TOC at a minimum, it is alsoimportant to keep the amount of organic tertiary amine in the ammoniumsulfate composition as low as possible. The TOC may be determinedaccording to standard method DIN EN 1484-113.

In other conventional processes, ammonia may be utilized as theinorganic base to treat the process stream. In these processes, however,all of the ammonia that is fed to the recovery process may not react,thus resulting in unreacted ammonia. This unreacted ammonia isproblematic from efficiency and environmental perspectives.Specifically, the unreacted ammonia in the treated stream may havedetrimental effects on the ability to further separate impurities fromthe solvents.

Thus, even though conventional processes may treat the sulfuricacid-containing process streams with inorganic bases such as ammonia torecover tertiary amines and to produce ammonium sulfate, the needremains for an improved process that provides for more efficientrecovery of the solvents in the treated stream.

All of the references discussed above are hereby incorporated byreference.

SUMMARY OF THE INVENTION

The present invention, in one embodiment, is to a process for producingan ammonium salt composition. The process comprises the step ofproviding a process stream comprising sulfuric acid, methylenedichloride, and a tertiary amine (or a precursor thereof). The processfurther comprises the step of contacting the process stream with ammoniaunder conditions effective to form a product stream and a waste stream.The product stream may comprise the ammonium salt and the waste streammay comprise water, methylene dichloride, ammonia, and the tertiaryamine. The process further comprises the step of deriving from the wastestream an off gas stream comprising ammonia and methylene dichloride,e.g., a first amount of methylene dichloride. Preferably, the processfurther comprises the step of contacting the off gas stream with an acidunder conditions effective to reduce the amount of ammonia therein. Theprocess further comprises the step of contacting at least a portion ofthe off gas stream or a derivative thereof with an adsorbent underconditions effective to separate the least a portion of the off gasstream or a derivative thereof into a methylene dichloride streamcomprising methylene dichloride.

In another embodiment, the invention is to a process for treating an offgas stream from a potassium acesulfame production process. The processcomprises the step of forming the off gas stream comprising a firstamount of ammonia and a first amount of methylene dichloride. Theprocess further comprises the step of treating the off gas stream withan acid to form a treated off gas stream comprising a reduced amount ofammonia. The process further comprises the step of contacting thetreated off gas stream with an adsorbent to form a methylene dichloridestream comprising methylene dichloride.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail below with reference to theappended drawing.

FIG. 1 shows an ammonium sulfate production process in accordance withan embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Introduction

Conventional processes may treat process waste streams that comprisesulfuric acid, organic tertiary amines, and solvents, e.g., methylenedichloride, with ammonia 1) to separate the organic tertiary amines and2) to produce ammonium sulfate, which is commercially valuable in thefertilizer industry. Typically, the solvent in the process streamremains from reactions that have taken place prior to formation of theprocess stream. In a preferred embodiment, the solvent is methylenedichloride, which remains in the process stream from an acesulfame-Kproduction process. These conventional processes, however, yield highamounts of unreacted ammonia. This unreacted ammonia typically hasdetrimental effects on the ability to further separate the components ofthe treated stream. As one example, the unreacted ammonia adverselyaffects the distillation of impurities from the methylene dichloridesolvent due to the similar boiling points of ammonia and methylenedichloride. Also, methylene dichloride streams that contain unreactedammonia may not be re-used in some production processes, e.g.,acesulfame-K production processes. As a result, the conventional treatedmethylene dichloride contains a high level of impurities, e.g., ammonia,and cannot be recycled and/or re-used without costly additionalseparation.

The present invention relates to the production of ammonium sulfate froma process stream that comprises sulfuric acid, organic tertiary amines(or precursors thereof), and solvent, e.g., methylene dichloride. In theinventive process, sulfuric acid in the process stream is reacted withammonia in a primary reaction unit to form a first amount of ammoniumsulfate. Preferably, an excess of ammonia is utilized to maintain a pHvalue favorable for the formation of the desired products. It has nowbeen discovered that unreacted ammonia remains from the sulfuricacid-ammonia reaction and that this unreacted ammonia may be treatedwith sulfuric acid, e.g., in a secondary reaction unit, to form ammoniumsalt(s), e.g., additional ammonium sulfate. As a result, the residualammonia in the treated process stream beneficially is reduced.Accordingly, 1) impurities may be more effectively separated from themethylene dichloride, e.g., via adsorption/desorption, 2) less ammoniamay be present in the separated methylene dichloride stream, and 3) ahigher purity methylene dichloride stream may be produced without theneed for subsequent purification. The high purity methylene dichloridestream then may be recycled and/or re-used.

Generally speaking, the present invention may be utilized to recoverfrom the sulfuric acid stream any tertiary amines. In one embodiment,the tertiary amines are those comprising up to 20 carbon atoms pernitrogen atom, e.g., up to 12 carbon atoms. Examples of the amines thatcan be recovered from the process sulfuric acid stream are selected fromthe group comprising trimethylamine, triethylamine, diethyipropylamine,tri-n-propylamine, triisopropylamine, ethyldiisopropylamine,tri-n-butylamine, triisobutylamine, tricyclohexylamine,ethyldicyclohexylamine, N,N-dimethylaniline, N,N-diethylaniline,benzyldimethylamine, pyridine, substituted pyridines such as picoline,lutidine, cholidine or methylethylpyridine, N-methylpiperidine,N-ethylpiperidine, N-methylmorpholine, N,N-dimethylpiperazine,1,5-diazabicyclo[4.3.0]-non-5-en, 1,8-diazabicyclo-[5.4.0]-undec-7-en,1,4-diazabicyclooctane, tetramethylhexamethylendiamine,tetramethylethylendiamine, tetramethylpropylendiamine,tetramethylbutylendiamine, 1,2-dimorpholylethan,pentamethyldiethyltriamine, pentaethyldiethylentriamine,pentamethyldipropylentriamine, tetramethyldiaminomethane,tetrapropyldiaminomethane, hexamethyltriethylentetramine,hexamethyltripropylenetetramine, diisobutylentriamine andtriisopropylentriamine. Preferably, the tertiary amine comprisestriethylamine.

The ammonia that can be reacted with the process stream, in someembodiments, may be used in gaseous or liquid form. In one embodiment,the partial pressure of the ammonia ranges 0.01 MPa to 30 MPa e.g., from0.1 MPa to 10 MPa, and is limited only by the compressive strength ofthe equipment that is used. The ammonia may be used neat or as a mixturewith other gases. The ammonia, in one embodiment, may be used as asolution in other solvents, preferably as an aqueous solution, and theaqueous solution may be obtained commercially or may be produceddirectly from the reaction by introducing gaseous or liquid ammonia inwater. The heat of solution that is generated may either be removed orretained by transferring the heated solution to the following reactionstep. To avoid the exhalation of ammonia, it is preferred to work atelevated pressure, e.g. a pressure greater than 0.1 MPa, e.g., greaterthan 1 MPa. In a preferred embodiment, to recover organic tertiaryamines from the sulfuric acid stream, ammonia in gaseous or dissolvedform may brought to the reaction with the sulfuric acid streamcomprising the organic tertiary amines. Preferably, the ammonia is mixedwith the sulfuric acid in an amount sufficient to obtain a pH greaterthan 9.5, e.g., greater than 10 or greater than 10.5. According to apreferred embodiment, the pH in the sulfuric acid-ammonia reactionranges 9.8 to 12, e.g., from 10 to 11.5. In one embodiment, the ammoniais added to the sulfuric acid in an amount sufficient to obtain theseranges.

Suitable process streams that may be utilized in the inventive processpreferably contain from 0.1 wt % to 100 wt % of tertiary amines(optionally in the precursor form of the respective organyl ammoniumhydrogen sulfate), e.g., from 1 wt % to 75 wt % or from 10 wt % to 50 wt%. Solutions may also contain free sulfuric acid and water. In oneembodiment the process stream for example, comprises 35 wt %triethylammonium hydrogen sulfate, 45 wt % sulfuric acid, 16 wt % water,and minor amounts of organic components.

Without being bound by theory, it is believed that during the reactionof sulfuric acid with ammonia, the free sulfuric acid is neutralized.This neutralization may be followed by conversion of organyl ammoniumhydrogen sulfate to the corresponding amines. The reaction may beconducted batchwise, e.g. in an agitating machine, or continuously,e.g., in a pump reactor with or without agitation means. In the lattercase, a static mixer is also a suitable reactor. In this case, thestatic mixer may be equipped with a temperature equalizer. Preferably,the reaction is conducted in a plug flow reactor. The plug flow reactoris preferred because it allows the reaction to be conducted at elevatedpressure and elevated temperature.

The reaction preferably is conducted at an elevated pressure, e.g., from0.2 MPa to 1.2 MPa or from 0.7 MPa to 1.0 MPa. The reaction preferablyis conducted at temperatures ranging from 95° C. to 150° C., e.g., from100° C. to 140° C. or from 110° C. to 130° C.

In one embodiment, in order to avoid precipitation of the ammoniumsulfate by exceeding the solubility limit during or after the reaction,water is added to the reaction mixture. This addition may be performedby diluting the employed sulfuric acid with water before the reaction,by adding water during the reaction, or by diluting the obtainedammonium sulfate solution after completion of the reaction.

The reaction heat that is produced may be removed using typical coolingdevices known in the art. According to a preferred embodiment, however,the released reaction heat is used in a subsequent separation step,e.g., in a distillation of the organic tertiary amines. In case thereaction has been conducted under pressure and elevated temperature, theexpanded reaction mixture may be directly conveyed to a distillationcolumn. Preferably, the inventive process is performed at temperaturesat or above the boiling point of the free amine, or at or above theboiling point of the amine/water azeotrope, if this azeotrope ispresent. For example, in the case of triethylamine, the preferredtemperature ranges from 75° C. to 105° C. at 1 bar. In case the reactionheat is not sufficient for distillation, additional heating may beutilized.

In another embodiment, the energy from the reaction is at leastpartially used to evaporate the water in the ammonium sulfate to yieldsolid ammonium sulfate, e.g., the reaction heat may be used to evaporatewater from the aqueous ammonium sulfate solution that is produced.

In one embodiment, the organic tertiary amines formed in the sulfuricacid-ammonia reaction are separated from the reaction mixture. Inpreferred embodiments, during the separation, the pH of the reactionmixture is adjusted at a pH greater than 9.5, e.g., greater than 10 orgreater than 10.5. Preferably the pH is adjusted such that the pH rangesfrom 9.8 to 12, e.g., from 10 to 11.5.

The separation of the released amines from the reaction mixture, in oneembodiment, may be performed by distillation, extraction, and/or phaseseparation. Distillation is preferred for amines having a low boilingpoint and/or amines having good water solubility. Distillation also ispreferred where the amines form an azeotrope with water. Distillationmay be performed directly from the reaction vessel or in a two stageapparatus.

According to a preferred embodiment, the thermal energy of the productsobtained at the head of the distillation column may be used to heat thefeed flow, e.g. the ammonia feed or the feed comprising the reactionmixture.

In one embodiment, low solubility amines that are in the ammoniumsulfate solution may be separated through phase separation. In anotherembodiment, the ammonium sulfate solution is extracted with a suitablesolvent. Preferably, the organic tertiary amine is separated from thereaction mixture by extraction with an organic liquid, preferably aliquid hydrocarbon. In one preferred embodiment, the organic liquidcomprises an aliphatic liquid hydrocarbon comprising at least 8 carbonatoms, e.g., at least eight carbon atoms, most preferably being octane.The methods for the separation of the organic amines may be appliedindividually or in combination.

In one embodiment, the organic tertiary amine, e.g., triethylamine, isseparated from the sulfuric acid-ammonia reaction mixture in adistillation column and, in order to maintain a pH of 9.5 or higherduring the separation in the distillation column, ammonia is addedthereto. Preferably, the ammonia is added to the distillation columncounter to the flow the reaction mixture. In one embodiment, during thedistillation, the sulfuric acid-ammonia reaction mixture is continuouslyfed to the upper part of a distillation column and the ammonia iscontinuously fed at the lower part or the middle part of thedistillation column. The position of the ammonia feed may be used tocontrol the pH of the reaction mixture being separated. The amount ofammonia and, consequently, the adjusted pH value, influence the capacityof the column with respect to separation of the tertiary amines from theaqueous ammonium sulfate solution. The closer the ammonia feed is to thebottom of the distillation column, the higher the pH of the reactionmixture in the bottom of the column.

Also, the position of the ammonia feed to the distillation column alsomay influence the pH of the aqueous solution comprising ammoniumsulfate, which exits the bottom of the separation unit, e.g.,distillation column. In a preferred embodiment, the ammonia feed ispositioned on the distillation column such that the aqueous ammoniumsulfate solution, which is essentially free of the organic tertiaryamine, in the lower part of the column has a pH ranging from 5 to 7,e.g., from 5.5 to 6.5.

In one embodiment, the inventive process further comprises the step ofdewatering the recovered tertiary amine, which can optionally befollowed by further distillation of the dewatered amine. Preferably, theorganic tertiary amine, e.g., triethylamine, is recovered in a yield ofat least 99.0%, e.g., at least 99.5% or at least 99.9%.

In another embodiment, the inventive process forms ammonium sulfate asproduct. The ammonium sulfate solution, thus formed, provides a quicklyrecoverable, easily dosable, valuable nitrogen fertilizer. In oneembodiment, no additional processing of the ammonium sulfate is requiredprior to use. The ammonium sulfate content of the solution may becontrolled by adjusting 1) the water content of the reactant sulfuricacid, 2) the addition of water before, during or after the reaction,and/or 3) distillation of water taking into account the solubility limitof ammonium sulfate in water. In one embodiment, the ammonium sulfatesolution is purified, e.g., distilled or spray dried, to removesubstantially all of the water therefrom. The solid ammonium sulfate,thus produced, may be used as a fertilizer.

The reaction of the ammonia and the sulfuric acid, as discussed above,yields a product mixture comprising water, the tertiary amine, solvent,e.g., methylene dichloride, ammonia, e.g., unreacted ammonia, andammonium salt, e.g., ammonium sulfate. Preferably, the subsequentseparation step yields a waste stream comprising water, methylenedichloride, the tertiary amine, and ammonia, and a product streamcomprising ammonium salt, e.g., a first amount of ammonium salt.

The inventive process, in some embodiments, further comprises the stepof deriving from the waste stream an off gas stream comprising ammonia,e.g., a preliminary amount of ammonia, and a first amount of methylenedichloride. Thus, the waste stream may be processed to separate, amongothers, the unreacted ammonia, the methylene dichloride, and/or thetertiary amine(s) therefrom. The preliminary amount of ammonia in theoff gas preferably comprises at least a portion of the unreacted ammoniathat remains from the ammonia utilized to contact the process stream. Insome embodiments, the off gas is derived directly from the reactionvessel. Preferably, the reaction mixture is condensed to yield a liquidstream and a vapor stream. The liquid stream may be directed to adecanter and the vapor stream, which comprises unreacted ammonia andmethylene dichloride, may be directed to further processing. Inpreferred embodiments, the off gas comprises at least a portion of thevapor stream.

In one embodiment, at least a portion of the off gas stream or aderivative of the off gas, is contacted with an adsorbent underconditions effective to separate the at least a portion of the off gasstream or a derivative of the off gas into a methylene dichloride streamcomprising methylene dichloride and a discard stream comprising purifiedair. Preferably, the methylene dichloride stream, as formed, comprisesat least 75 mole % methylene dichloride, e.g., at least 90 mol % or atleast 95 mol % and less than 10 mol % impurities, e.g., less than 5 mol% or less than 3 mol %. In one embodiment, the discard stream comprisesless than 1 mol % methylene dichloride, e.g., less than 0.5 mol % orless than 0.1 mol %. Thus, by contacting the off gas with the adsorbent,a high purity methylene dichloride stream is formed, which can berecycled and/or re-used without additional separation. Further, becauselittle or no methylene dichloride is present in the discard stream, verylittle if any methylene dichloride is wasted, e.g., purged from thesystem.

In some embodiments, the process further comprises the step ofcontacting the off gas stream with an acid, e.g., sulfuric acid, underconditions effective to form an ammonium salt stream and a purge stream.In doing so, at least 75 mol % of the ammonia in the off gas may beconverted, e.g., at least 95 mol % or at least 98 mol %. In a preferredembodiment, the off gas is contacted with the acid in at least onesecondary reaction unit, e.g., a reactive distillation column or awashing column. In one embodiment, the secondary reaction unit comprisesa washing column, which employs a sulfuric acid washing agent. Thesecondary reaction may, also comprise multiple reactions units, e.g.,multiple reactors and/or multiple columns. In one embodiment, the offgas is contacted in a reactive distillation column and any remainingunreacted ammonia is further reacted with sulfuric acid in a washingvessel. Preferably, this contacting step is performed before the off gasstream or derivative thereof is contacted with the adsorbent. In thesecases, the purge stream, which is a derivative of the off gas stream,then is contacted with the adsorbent. Advantageously, the reduced amountof ammonia in the purge stream allows a more efficient separation ofimpurities from the methylene dichloride. The high purity methylenedichloride stream is thus produced.

Exemplary Ammonium Salt Production Process

FIG. 1 shows an exemplary ammonium salt production process in accordancewith some embodiments of the present invention. Process stream 100comprises sulfuric acid, at least one tertiary amine (optionally in theform of the respective organyl ammonium hydrogen sulfate), methylenedichloride, and water. In a preferred embodiment, process stream 100 isa waste stream from an acesulfame-K production process, e.g., at least aportion of an aqueous sulfuric acid phase from an acesulfame-Kproduction process, as discussed below. Exemplary ranges for some of thecomponents of the process stream are shown in Table 1.

TABLE 1 PROCESS STREAM COMPOSITION Conc. (mol %) Conc. (mol %) Conc.(mol %) Sulfuric Acid 1 to 99 30 to 65 35 to 55 Trialkylammonium 1 to 7525 to 45 30 to 40 Ammonium Hydrogen Sulfate Methylene Dichloride 1 to 99 1 to 50  2 to 10 Water 1 to 99  5 to 50 10 to 25 Organics Less than 1Less than 0.5 Less than 0.1

As shown in FIG. 1, pre-reaction zone 102 receives process stream 100.Pre-reaction zone 102 prepares the reactants, e.g., sulfuric acid,water, and ammonia, for separation of the tertiary amines and/orconversion of sulfuric acid to ammonium sulfate. In one embodiment, inpre-reaction zone 102, ammonia, e.g., gaseous ammonia, is fed to a firstplug flow reactor, where the ammonia is diluted with water. The watermay be provided to the first plug flow reactor from a water reservoir.The aqueous ammonia solution, thus formed, exits the first plug flowreactor is conveyed to a second plug flow reactor, where the ammoniasolution contacts the acesulfame-K waste stream. The waste stream fed tothe second plug flow reactor may be fed from a waste stream reservoir.The acesulfame-K waste stream/ammonia product stream exits the secondplug flow reactor, thus exiting pre-reaction zone 102, and is directedvia line 104 to reactor 106.

In reactor 106 sulfuric acid from the process stream contacts, e.g.,reacts with, ammonia to form ammonium sulfate. In some embodiments, atleast 50% of the sulfuric acid in process stream 100 is converted toammonium sulfate in reactor 106, e.g., at least 90% or at least 95%.Reactor 106 preferably yields a crude product comprising ammoniumsulfate, triethylammonium sulfate, triethylamine, water, and unreactedammonia. Reactor 106 is preferably a plug flow reactor, but othersuitable reactor types, such as a stirred tank reactor or othertube-style reactors, may be employed as well. The reaction in reactor106 is, in one embodiment, conducted under an elevated pressure, forexample at a pressure ranging from 2 to 12 bar, e.g., from 7 to 10 bar,and at temperatures ranging from 95° C. to 140° C., e.g., from 100° C.to 126° C. or from 110° C. to 130° C.

In preferred embodiments, this reaction is carried out under basicconditions, e.g., the reaction is maintained at a high pH. In oneembodiment, the pH of the reaction mixture is maintained at a level atleast 8, at least 9, at least 9.5 or at least 10. In terms of ranges,the pH of the reaction mixture may be maintained at a level ranging from8 to 12, e.g., from 9 to 12, or from 10 to 11.5. In one embodiment, thehigh pH level is maintained by mixing ammonia with the waste sulfuricacid. Maintaining the pH at these levels provides for 1) efficienttertiary amine separation, 2) efficient sulfuric acid conversion, and 3)a product ammonium sulfate having a low TOC, e.g., less that 1 wt %organic content or less than 0.5 wt % organic carbon content, based onthe total amount of dried ammonium sulfate obtained.

In a preferred embodiment, water is added to the reaction mixture toavoid precipitation of ammonium sulfate, which occurs as the solubilitylimit is exceeded during or after the reaction. This precipitation maybe avoided, for example, by diluting process stream 100 with water priorto reactor 106, or by adding water to reactor 106, or by diluting thereaction solution.

Although FIG. 1 shows one reactor, there may be multiple reactors forreacting the process stream and aqueous ammonia stream.

In a preferred embodiment, the sulfuric acid and the ammonia are reactedin reactor 106 and are further reacted and/or separated in separationunit 110, e.g., a reactive distillation column. In this case, thereaction mixture exits reactor 106 and is directed via line 108 toseparation unit 110. Separation unit 100 is preferably a distillationcolumn, e.g., a reactive distillation column, however, other suitableseparation units, such as extractors and phase separators may beemployed. Distillation is especially advantageous in cases where theamines in the product stream have a low boiling point, are highlysoluble in water, and/or form an azeotrope with water. Although FIG. 1shows a single separation unit, multiple separation units may also beemployed.

In one embodiment, separation unit 110 is operated under basicconditions. Preferably, these basic conditions are achieved by addingammonia, e.g., via ammonia feeds 112. In one embodiment, the pH of thedistillation fluid in separation unit 110 is maintained at a level atleast 8, at least 9, at least 9.5 or at least 10. In terms of ranges,the pH of the distillation fluid may be maintained at a level rangingfrom 8 to 12, e.g., from 9 to 12, or from 10 to 11.5. Also, ammonia maybe added to react with sulfuric acid present in separation unit 110 toform ammonium sulfate. Ammonia is added in a molar excess in separationunit, such that the molar ratio of ammonia to sulfuric acid is greaterthan 1.2:1, e.g., greater than 1.5:1. The excess molar ratio is neededto ensure complete reaction of the sulfuric acid.

Separation unit 110 yields a residue comprising an ammonium salt, e.g.,ammonium sulfate, which exits separation unit 110 via line 114, and adistillate comprising triethylamine, water, unreacted ammonia, methylenedichloride, and acetone. In one embodiment, the distillate comprises atriethylamine-water azeotrope.

The distillate from separation unit 110, in one embodiment, is condensedto yield a liquid stream and a vapor stream. The liquid stream isconveyed to phase separation unit 116, which is preferably a decanter.Phase separation unit 116 separates the liquid phase of the distillateinto upper liquid organic phase 118, which comprises triethylamine, andlower liquid aqueous phase 120, which comprises water. The vapor stream,e.g., at least a portion of the off gas, comprising methylene dichlorideand ammonia, e.g., a preliminary amount of ammonia, exits separationunit 110 and, once separated from the liquid phase, is directed tofurther processing. In one embodiment, the off gas further comprisesacetone. In one embodiment, the off gas comprises from 1 mol % to 50 mol% methylene dichloride, based on the total weight of the off gas, e.g.,from 1 mol % to 25 mol % or from 1 mol % to 10 mol %. In terms of upperlimits, the off gas may comprise less than 50 mol % methylenedichloride, e.g., less than 25 mol % or less than 10 mol %. It isappreciated that the off gas will contain some amount of methylenedichloride. In terms of lower limits, the off gas may comprise at least0.1 mol % methylene dichloride, e.g., at least 1 mol % or at least 5 mol%. In one embodiment, the off gas comprises from 25 mol % to 99.9 mol %ammonia, based on the total weight of the off gas, e.g., from 50 mol %to 99 mol % or from 75 mol % to 98 mol %. In terms of upper limits, theoff gas may comprise less than 99.9 mol % ammonia, e.g., less than 99mol % or less than 98 mol %. It is appreciated that the off gas maycontain a significant amount of ammonia. In terms of lower limits, theoff gas may comprise at least 50 mol % ammonia, e.g., at least 75 mol %or at least 90 mol %.

Upper liquid organic phase 118 is directed via line 124 to column 126,which preferably is a dewatering column. Column 126 separates upperliquid organic phase 118 into a distillate comprising awater/triethylamine azeotrope and optionally ammonia and a residuecomprising triethylamine. At least a portion of the water/triethylamineazeotrope is recycled to phase separation unit 116 via line 128. In oneembodiment, at least a portion of the ammonia in the distillate ofcolumn 126 is combined with line 122 via optional line 130 to formcombined ammonia feed line 132. The triethylamine-containing residue isdirected via line 134 to column 136, which is preferably a distillationcolumn. Column 136 separates the contents of line 134 into atriethylamine distillate and a residue comprising high boiling pointorganic compounds. The distillate from column 136 comprises purifiedtriethlyamine is withdrawn via line 138 and is optionally recycled to anacesulfame-K production process (not shown). The residue exits column136 via line 140 and is disposed accordingly.

The off gas in line 122 exiting phase separation unit 116 is optionallycombined with ammonia in line 130 and directed to column 142 via line132. Column 142 is, for example, a washing column or a reactivedistillation column. In column 142, the ammonia-containing off gas iscontacted with sulfuric acid from sulfuric acid feed 144 to form ammoniasalts, e.g., ammonium sulfate. The ammonium sulfate exits column 142 asa residue via line 148. Preferably, the ammonium sulfate-containingresidue from column 142 is recycled to separation unit 110 (viapre-reaction zone 102), where the additional ammonium sulfate may berecovered in the residue of separation unit 110. Water may also beprovided to column 142 via water feed 146. Unreacted ammonia, if any,exits column 142 as an exhaust distillate, e.g., a purge stream, vialine 150. Preferably, 1) the acid is provided to column 142 in a firstzone, wherein acid reacts with the ammonia to form the ammonium salts;and 2) water is added in a second zone to dissolve any remainingammonia.

Preferably, the reaction in the secondary reactor is conducted in aneutral or acidic environment so as to better neutralize the ammoniabeing fed thereto. In one embodiment, the pH in the secondary reactor isless than 8, e.g., less than 7, or less than 6. In terms of ranges, thepH in the secondary reactor may be maintained at a level ranging from0.1 to 8, e.g., from 1 to 6.

In a preferred embodiment, multiple units are utilized to react theammonia in the off gas with ammonia to form ammonium sulfate. As oneexample (not shown), an additional washing unit may be employed to reactunreacted ammonia that remains in the exhaust distillate. The additionalwashing unit may be any suitable unit, preferably being a washing vesselhaving an acid feed.

In other embodiments, the off gas is contacted in a suitable reactionunit other than a column, e.g., a reactor, a scrubber, a spray tower, ora tube-style reactor. Methods of contacting the reactants are well knownin the art and it is well within the skill of the art to utilize anappropriate unit to perform the contacting step.

As a result of the secondary reaction of acid with the unreacted ammoniain line 132, additional ammonium sulfate is advantageously formed.Conventionally, the unreacted ammonia in line 132 would be purged orotherwise disposed. As such, column 142 provides an exhaust distillatethat exits via line 150 and comprises little, if any ammonia, e.g., lessthan 10 mol % ammonia, less than 5 mol % ammonia, or less than 3 mol %ammonia. The distillate in line 150 may also comprise a significantportion of any solvents that may be used throughout the inventiveprocess or that may be present in the initial process stream, e.g.,methylene dichloride. In one embodiment, exhaust distillate 150comprises methylene dichloride and a reduced amount of ammonia (ascompared to the preliminary amount of ammonia). In one embodiment, thereduced amount of ammonia is at least 90% less than the preliminaryamount of ammonia, e.g., at least 95% or at least 98%. In anotherembodiment, the exhaust distillate stream comprises no ammonia, e.g.,the preliminary amount of ammonia is reduced to nothing. As a result ofthe ammonium sulfate formation from the unreacted ammonia, a low ammoniacontent exhaust distillate exits column 142 and may be released safely.

As a result of the secondary reaction step, a high percentage of thetotal amount of ammonia fed to the process is converted, preferably, atleast 90 mol % of a total amount of ammonia fed to the process, e.g., atleast 95 mol % or at least 98 mol %. In these embodiments, the totalamount of ammonia comprises all of ammonia streams fed to the processincluding ammonia in the process stream, ammonia fed to pre-reactionzone 102, and the ammonia fed via ammonia feed line(s) 112. In oneembodiment, because the unreacted ammonia is converted rather than beingwasted, the reduced amount of ammonia in the line 150 is less than 10%of a total amount of ammonia fed to the process, e.g., less than 5% orless than 3%. In some embodiments, the expected overall ammonium saltproduction is based on the conversion of sulfuric acid in the wastestream and the ammonium salt selectivity. Thus, the expected productionof ammonium sulfate (in moles) in these instances, would be the moles ofsulfuric acid converted multiplied by the ammonium salt selectivity.Preferably, the overall ammonium salt production is greater than theexpected production of ammonium salt, e.g., at least 10% greater, atleast 15% greater, or at least 25% greater.

In preferred embodiments, the acid used to contact the off gas issulfuric acid, and the resultant ammonium salt comprises ammoniumsulfate. However, in other embodiments, acids other than sulfuric acidmay be employed. In such cases, the resultant ammonium salt willcorrespond to the acid that is employed. For example, if phosphoric acidwere utilized, the resultant ammonium salt would comprise ammoniumphosphate.

The contents of line 150 then may be further processed to recover thecomponents thereof. The purge stream exiting column 142, e.g., line 150,comprises a significant amount of methylene dichloride, otherimpurities, e.g., organics, nitrogen, acetone, and water, a reducedamount of ammonia, if any, and air. In preferred embodiments, at least aportion of the purge stream in line 150 is directed to column 152, whichpreferably is an adsorber column, which utilizes an adsorbent toseparate a purified air stream from the methylene dichloride and othercomponents of line 150. The adsorbent may be provided via adsorbent feed157. Thus, column 152 separates the purge stream into a methylenedichloride stream and a discard stream. The methylene dichloride streamcomprises methylene dichloride, adsorbent, and optionally acetone,organics, and water and exits column 152 via line 154. The discardstream comprises purified air and a small amount, if any, methylenedichloride e.g., less than 1 mol % or less than 0.5 mol % and exitscolumn 152 via line 156. Preferably, the adsorbent comprisespolyethylene glycol ether. As discussed above, the presence of ammoniatypically has a detrimental effect on the separation of the impuritiesfrom the methylene dichloride. In the present invention, however, theefficiency of the separation is beneficially improved due to the reducedamount of ammonia in the purge stream.

In one embodiment, the methylene dichloride/adsorbent composition inline 154 is separated, e.g., desorbed, to yield a purified methylenedichloride stream comprising methylene dichloride and optionally smallamounts of acetone, organics, and water and an adsorbent recycle streamcomprising the adsorbent. In this step, the adsorbent is separated fromthe remaining components of the dichloride/adsorbent composition.Preferably, the desorption is achieved via column 158, e.g., adesorption column, which utilizes a desorbent, which may be fed viadesorbent feed 160. Preferably, the desorbent comprises steam. Theseparated adsorbent is optionally recycled to column 152, e.g., via line162. In preferred embodiment, the purified methylene dichloride streamexits column 158 via line 164 and comprises at least 75 mol % methylenedichloride, e.g., at least 90 mol % or at least 95 mol %. The purifiedmethylene dichloride stream may further comprise less than 10 mol %impurities, e.g., less than 5 mol % or less than 3 mol %, and less than10 mol % adsorbent, e.g., less than 5 mol % or less than 3 mol %. In apreferred embodiment, the purified methylene dichloride stream compriseslittle, if any, ammonia, e.g., less than 1 mol %, less than 0.5 mol %,or less than 0.1 mol %.

Of course, the adsorption/desorption separation scheme of FIG. 1 ismerely exemplary and it is within the contemplation of the presentinvention to utilize other suitable adsorption/desorption systems.

Because the purified methylene dichloride stream comprises a smallamount, if any, impurities and/or ammonia the purified methylenedichloride stream advantageously may be recycled or re-used withoutfurther separation, which is required in conventional methylenedichloride streams. Preferably, the purified methylene dichloride streamis recycled to the acesulfame-K process discussed herein. In someembodiments, very little, if any methylene dichloride is wasted, e.g.,purged, from the system. Preferably, less than 1% of the total methylenedichloride provided to the process is purged therefrom, e.g., less than0.5% or less than 0.1%.

The ammonium sulfate production process of the present invention may beused with any suitable process stream comprising a suitable acid. In apreferred embodiment, the process stream comprises an acesulfame-K wastestream that results from an acesulfame-K production process. Oneexemplary process reacts sulfamic acid and/or a salt thereof anddiketene to form an acetoamide salt, e.g., acetoacetamide-N-sulfonatetriethylammonium salt. In preferred embodiments, the acetoamide saltserves as an intermediate in the formation of the cyclized acesulfame-H.The reaction product containing the acetoacetamide salt is thencyclized, preferably utilizing sulfur trioxide. The cyclized product isthen hydrolized to form acesulfame-H, the acid form of acesulfame-K. Thehydrolysis reaction is preferably carried out via addition of water (orice) and optionally aqueous sulfuric acid.

The hydrolysis reaction yields a multiple phase mixture, which isdirected to a phase separation unit, e.g., decanter. The decanterseparates the multiple phase mixture into an organic phase, an aqueousphase (sulfuric acid phase), and optionally a solid precipitate phase.The aqueous phase comprises sulfuric acid and at least one tertiaryamine. As such, this aqueous phase may serve as a process stream for usein embodiments of the present invention.

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references discussed above in connection withthe Background and Detailed Description, the disclosures of which areall incorporated herein by reference. In addition, it should beunderstood that aspects of the invention and portions of variousembodiments and various features recited below and/or in the appendedclaims may be combined or interchanged either in whole or in part. Inthe foregoing descriptions of the various embodiments, those embodimentswhich refer to another embodiment may be appropriately combined withother embodiments as will be appreciated by one of skill in the art.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way, of example only, and is not intended tolimit the invention.

1. A process of producing an ammonium salt composition, comprising thesteps of: (a) providing a process stream comprising sulfuric acid,methylene dichloride, and a tertiary amine or a precursor thereof; (b)contacting the process stream with ammonia under conditions effective toform a product stream comprising the ammonium salt and a waste streamcomprising water, methylene dichloride, ammonia, and the tertiary amine;(c) deriving from the waste stream an off gas stream comprising ammoniaand a first amount of methylene dichloride; and (d) contacting at leasta portion of the off gas stream or a derivative thereof with anadsorbent under conditions effective to separate the least a portion ofthe off gas stream or a derivative thereof into a methylene dichloridestream comprising methylene dichloride.
 2. The process of claim 1,wherein step (d) forms the methylene dichloride stream comprising atleast 90 mol % methylene dichloride and at least a portion of theadsorbent and a discard stream comprising air.
 3. The process of claim2, further comprising separating the methylene dichloride stream to forma purified methylene dichloride stream and an adsorbent recycle streamcomprising at least a portion of the adsorbent.
 4. The process of claim2, wherein the discard stream comprises less than 1 mol % methylenedichloride.
 5. The process of claim 3, wherein step (d) is performed inan adsorption/desorption system comprising an adsorption column and adesorption column.
 6. The process of claim 5, wherein the adsorbentrecycle stream is recycled to the adsorber column.
 7. The process ofclaim 3, wherein the purified methylene dichloride stream comprises lessthan 10 mol % impurities.
 8. The process of claim 3, wherein thepurified methylene dichloride stream is recycled to a potassiumacesulfame production process.
 9. The process of claim 1, furthercomprising contacting the off gas stream with an acid under conditionseffective to reduce the amount of ammonia therein.
 10. The process ofclaim 1, wherein the adsorbent comprises polyethylene glycol ether. 11.The process of claim 1, wherein the off gas further comprises nitrogen,acetone, organics, and water.
 12. The process of claim 1, wherein lessthan 1% of the total methylene dichloride provided to the process ispurged therefrom.
 13. A process for treating an off gas stream from apotassium acesulfame production process, comprising the steps of (a)forming the off gas stream comprising a first amount of ammonia and afirst amount of methylene dichloride; (b) treating the off gas streamwith an acid to form a treated off gas stream comprising a reducedamount of ammonia; and (c) contacting the treated off gas stream with anadsorbent to form a methylene dichloride stream comprising methylenedichloride and at least a portion of the adsorbent.
 14. The process ofclaim 13, wherein step (c) further forms a discard stream comprisingless than 1 mol % methylene dichloride.
 15. The process of claim 13,further comprising separating the methylene dichloride stream to form apurified methylene dichloride stream and an adsorbent recycle streamcomprising at least a portion of the adsorbent.
 16. The process of claim15, wherein the purified methylene dichloride stream comprises less than10 mol % impurities.
 17. The process of claim 16, wherein the purifiedmethylene dichloride stream is recycled to a potassium acesulfameproduction process.
 18. The process of claim 13, wherein the adsorbentcomprises polyethylene glycol ether.
 19. A process for producing anammonium salt composition, comprising the steps of: (a) providing aprocess stream comprising sulfuric acid, methylene dichloride, water,and a tertiary amine; (b) contacting the process stream with ammoniaunder conditions effective to form a product stream comprising theammonium salt and a waste stream comprising ammonia, water, the tertiaryamine, and the methylene dichloride, (c) deriving from the waste streaman off gas stream comprising a preliminary amount of ammonia andmethylene dichloride; (d) contacting the off gas stream with an acidunder conditions effective to form an ammonium salt residue streamcomprising ammonium salt and an overhead stream comprising methylenedichloride and a reduced amount of ammonia as compared to thepreliminary amount; and (e) contacting the overhead stream from step (d)with an adsorbent under conditions effective to form a methylenedichloride stream and a discard stream comprising air.
 20. The processof claim 19, further comprising separating the methylene dichloridestream to form a purified methylene dichloride stream and an adsorbentrecycle stream comprising the adsorbent.